Oral bacteria have been implicated in the development of chronic periodontitis. These organixms may initiate periodontal inflammation by producing antigens which activate the cellular immune responses of their host. The specific nature of the antigens is being investigated. The antigens produced by Actinomyces viscosus have been isolated and shown to be a series of complex heteropolymers composed of protein and carbohydrate. Several of these glycoproteins are highly immunogenic in rabbits but are unable to stimulate human peripheral blood lymphocytes. The rabbit humoral responses are specific for the carbohydrate portions of the molecule. However, one glycoprotein has been isolated which is at least as effective as whole cells in stimulating human peripheral blood lymphocytes. These studies may improve our understanding of the biochemical and immunological events which lead to chronic inflammation and destruction of periodontal tissues. BIBLIOGRAPHIC REFERENCE: Baker, J.J., Chan, S.P., Socransky, S.S., Oppenheim, J.J. and Mergenhagen, S.E.: Importance of Actinomyces and certain gram negative anaerobic organisms in the transformation of lymphocytes from patients with periodontal disease. Infect. Immun. 13: 1363-1368, 1976.